|Publication number||US7280507 B2|
|Application number||US 10/780,577|
|Publication date||Oct 9, 2007|
|Filing date||Feb 19, 2004|
|Priority date||Jul 15, 2003|
|Also published as||US20050013265|
|Publication number||10780577, 780577, US 7280507 B2, US 7280507B2, US-B2-7280507, US7280507 B2, US7280507B2|
|Inventors||Shinichirou Miyajima, Kazuhiro Ichiyanagi, Akiko Kusumoto, Yuji Nagano, Katsuhiro Eguchi, Naoyuki Takeshita, Yuji Ishii, Kazuyuki Inomoto|
|Original Assignee||Fujitsu Limited|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (10), Non-Patent Citations (1), Referenced by (2), Classifications (9), Legal Events (5)|
|External Links: USPTO, USPTO Assignment, Espacenet|
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2003-274463, filed on Jul. 15, 2003, the entire contents of which are incorporated herein by reference.
1) Field of the Invention
The present invention relates to a technique of transmitting data between a mobile station (client) and a relay-station that are connected by a radio local area network (radio LAN).
2) Description of the Related Art
In a conventional radio communication apparatus, when a relay station receives data properly from a mobile station, an acknowledgement signal is returned to the mobile station, in order to secure continuity of data transmitted between the mobile station and the relay station. The relay station does not transmit the acknowledgement signal if it does not receive the data properly. When an acknowledgement signal is not received from the relay station, the mobile station stores the data in a memory and retransmits the data with the next data to be transmitted.
In a technique disclosed in Japanese Patent Application Laid-open No. 2002-112341, a relay station transmits an acknowledgement signal to a mobile station, for each data received from the mobile station. In this technique, however, efficiency of data transmission deteriorates because of additional transmission of the response signal. Moreover, communication load increases due to the need of transmitting each response signal, particularly when data are transmitted near a bandwidth limit, or when only a transmission environment of very low bandwidth can be secured. Furthermore, the communication may be broken due to the excessive transmission load.
It is an object of the present invention to solve at least the problems in the conventional technology.
A radio LAN data transmission system according to one aspect of the present invention includes a host station, a relay station having a plurality of access points, and a mobile station having a radio LAN apparatus that transmits data to and receives data from the host station via the relay station. The radio LAN apparatus includes a memory unit that temporarily stores transmission data that is data to be transmitted to an access point; and a memory control unit that provides a control to store the transmission data in the memory unit at the time of switching from one access point to another access point, and to transmit the transmission data to the another access point when the radio LAN apparatus establishes a communication link with the another access point.
A radio LAN data transmission method according to another aspect of the present invention is a method of transmitting data between a mobile station having a radio LAN apparatus and a host station, via a relay station having a plurality of access points. The method includes temporarily storing transmission data in the radio LAN apparatus; detecting whether a link between the radio LAN apparatus and any one of the access points is established; reading the transmission data stored when it is detected at the detecting that a link between the radio LAN apparatus and any one of the access points has been established.
A computer program according to another aspect of the present invention realizes the method according to the above aspect on a computer.
The other objects, features, and advantages of the present invention are specifically set forth in or will become apparent from the following detailed descriptions of the invention when read in conjunction with the accompanying drawings.
Exemplary embodiments of the present invention are explained in detail below with reference to the accompanying drawings. The present invention is not limited to the embodiments.
An image recorded by a video camera installed in the mobile station 101 is coded by a compressing technique such as MPEG2, and is transmitted as image data to any one of the access points in the relay station 102 via the radio LAN. The access point that receives the image data from the mobile station 101 transmits the image data to the final access point. The final access point transmits the image data to the host station 103. The host station 103 decodes the image data transmitted by the mobile station 101 so as to monitor the image in real time.
An image recorded by the camera 201 is transmitted to the image processing section 203 for generating digitized image data. Sound acquired from the microphone 202 is transmitted to the sound processing section 204 for generating digitized sound data. The digitized image data and the digitized sound data are transmitted to the coding/decoding section 205 for coding. The coded data are transmitted to the memory control section 206. The memory control section 206 receives the coded data and stores them into the memory 207 one after another. The memory control section 206 reads the coded data stored in the memory 207 one by one, and transmits them to any one of the access points in the relay station 220 via the radio LAN interface 210. In the radio LAN apparatus 200, data are transmitted to an access point in the same sequence as the data are stored in the memory 207. In other words, the data are stored and read from the memory 207 in a first-in-first-out manner. The beacon detecting section 208 detects whether a link between the radio LAN apparatus 200 and the access points in the relay station 220 is established. The electrolytic strength detecting section 209 detects electrolytic strength of a radio wave transmitted from the access point in the relay station 220.
The relay station 220 has a plurality of access points. For example, a first access point 221, a second access point 222, a third access point 223, and a final access point 224 are shown in
The access point connected with the radio LAN apparatus 200 in the mobile station can be switched. Though the time required for the switching is about 0.5 to 3 seconds, but the communication with the access point is disconnected during this time. Thus, continuity of data transmission cannot be secured. Consider an example when the radio LAN apparatus 200 is moved from a communication range of the second access point 222 to a communication range of the third access point 223. If the communication between the radio LAN apparatus 200 and the second access point 222 is disabled, the memory control section 206 stops data transmission to the second access point 222 and keeps the transmission data stored in memory. At this time, as shown in
The data transmission method is explained next, with reference to the flowchart shown in
Each access point in the relay station 220 does not transmit a response confirmation signal, for acknowledging data, to the radio LAN apparatus 200. Therefore, transmission throughput does not deteriorate, and data can be transmitted at high rate.
The switching between the radio LAN apparatus 200 and each access point in the relay station 220 is executed by a conventional method.
When the mobile station crosses over communication ranges of different access points of the relay station, the access points are switched. In the configuration of the first embodiment, image data transmission is interrupted until the switching process is completed. When communication between the mobile station and the next access point is resumed, the data stored in the memory 207 of the radio LAN apparatus 200 are transmitted to the host station. As for the data that are received by the host station after the restarting of the communication, although a sequence of the data on the time axis is maintained, there is a possibility that there are intermittent coarse portions in the data and thus, quality of the image is degraded. A second embodiment of the present invention solves this problem.
At the final access point 224, the first signal processing section 303 receives data transmitted from an access point via the LAN interface 301. Because the data received by the first signal processing section 303 includes data obtained during switching of the access point, the data received are so-called burst data, which contains intermittent coarse portions (see
In the second embodiment, a transmission speed of the data input into the data smoothing section 305 is about 10 megabits per second, but a transmission speed of the data output from the data smoothing section 305 is about 6 megabits per second. With such throughput, the coarse portions between data are eliminated from the data output from the data smoothing section 305, and thus the smoothing of the data can be achieved (see
The transmission speed of the data input into the data smoothing section 305 and a transmission speed of the data output from the data smoothing section 305 are not limited to the above values. In the data smoothing section 305, the transmission speed of the output data should be less than that of the input data, so that the smoothing of the data can be achieved.
During the operation for switching the access point, as shown in
Suppose that data are transmitted between the radio LAN apparatus 200 of the mobile station and the second access point 222 of the relay station 220. When the mobile station moves to the communication range of the third access point 223, data transmission from the radio LAN apparatus 200 requires switching to the third access point 223. During the switching process, untransmitted data stored at the second access point 222 are transmitted to the third access point 223. When the time required for establishing the communication between the radio LAN apparatus 200 and the third access point 223 is shorter than an assumed time, the third access point 223 receives data from the radio LAN apparatus 200 before receiving the data from the second access point 222. In this case, the data received from the radio LAN apparatus 200 are transmitted to the final access point 224 before the data from the second access point 222. Thus, data is not transmitted in the correct sequence. A fourth embodiment of the present invention eliminates such a defect.
In the fourth embodiment, during the switching process, the memory monitoring section 305 a monitors the residual data quantity in the memory 306. When a quantity of data stored in the memory 306 becomes 0 (see
The data reading completion signal may be transmitted or received by the access points via the radio LAN interface 309 provided in the access point, or via a cable LAN.
Communication load increases because the data reading completion signal is transmitted every time the transmission of data is complete. Moreover, if data transmission increases, the efficiency of the communication is inhibited. A fifth embodiment of the present invention avoids such a problem. In the fifth embodiment, the data reading completion signal is not transmitted or received between the access points. Instead, a packet number written into a header section of the transmitted data is monitored. The packet numbers of the respective data are compared with each other so as to ensure that the data transmission order is maintained.
In the fifth embodiment, the first packet number detecting section 601 detects a packet number written into a header section of the data (see
The data to be transmitted also contains time stamps. Therefore, instead of comparing the packet numbers, time stamps may be compared. In this case, a first time stamp detecting section, a second time stamp detecting section, and a time stamp comparing section may be provided in
Just as data is transmitted from the mobile station to the host station, data can also be transmitted from the host station to the mobile station via the relay station. When the host station 230 transmits data via the relay station 220 to the radio LAN apparatus 200 in the mobile station, the data may contain intermittent coarse portions. Therefore, there is a possibility that the continuity of data transmission may be inhibited. A sixth embodiment of the present invention avoids such a defect.
According to the present invention, the bandwidth is used efficiently so that the data transmission efficiency can be improved. Therefore, even when transmission is executed near a bandwidth limit, or when a transmission environment of very low bandwidth can be secured the continuity of the data transmission is secured and the high quality of data transmission can be realized.
The radio LAN data transmission method can be realized by executing a program on a computer such as a personal computer or a workstation. This program may be recorded in a computer readable recording medium such as a hard disc, a flexible disc, a CD-ROM, a magneto optical (MO), or a digital versatile disk (DVD). The computer can execute the program after reading it from the recording medium. Further, the program may be a transmission medium, which can be distributed via a network such as the Internet.
The radio LAN data transmission system according to the present invention is useful for communication between the mobile station and the relay station via the radio LAN, and is particularly suitable when continuous transmission of real time data is required.
Although the invention has been described with respect to a specific embodiment for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art which fairly fall within the basic teaching herein set forth.
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|U.S. Classification||370/331, 370/338, 370/389, 370/328|
|International Classification||H04L12/28, H04W36/06, H04W36/08|
|Feb 19, 2004||AS||Assignment|
Owner name: FUJITSU LIMITED, JAPAN
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:MIYAJIMA, SHINICHIROU;ICHIYANAGI, KAZUHIRO;KUSUMOTO, AKIKO;AND OTHERS;REEL/FRAME:015005/0444;SIGNING DATES FROM 20040130 TO 20040202
|Mar 10, 2011||FPAY||Fee payment|
Year of fee payment: 4
|May 22, 2015||REMI||Maintenance fee reminder mailed|
|Oct 9, 2015||LAPS||Lapse for failure to pay maintenance fees|
|Dec 1, 2015||FP||Expired due to failure to pay maintenance fee|
Effective date: 20151009